This invention relates generally to off-road motor vehicles, such as tractors, and more particularly, to an oscillation stop mechanism, cooperable with a compound steering mechanism in which the front axle is pivotally moved in conjunction with the steering movement of the steerable wheels, to limit the amount of vertical oscillation of the front axle relative to the chassis of the tractor.
Tractors, whether used in an agricultural setting or in an industrial setting, typically include a fixed axle through which primary driving power is transferred through fixed wheels rotatably mounted on opposing ends of the fixed axle, and a steering axle having pivotally mounted steerable ground engaging wheels rotatably mounted on the opposing ends thereof to support the chassis of the tractor above the ground. Although supplemental driving power is often provided to the steerable ground engaging wheels, a steering mechanism remotely controllable by the operator from the operator's compartment selectively controls the pivotal movement of the steerable wheels relative to the steering axle.
One such steering mechanism incorporates a transversely disposed, horizontally extending hydraulic cylinder supported by the steering axle and connected to the opposing steerable wheels. This hydraulic cylinder affects pivotal movement of the steerable wheels about their respective pivotal connections to the steering axle by manipulating the pressures in the hydraulic cylinder to effect a transverse extension of cylinder rod, causing a turning of the wheels.
Due to physical limitations relating to the range of movement of the steering mechanism and to the eventual interference between the steerable wheels and the chassis or the steering axle, the amount of pivotal movement of the steerable wheels relative to the steering axle is limited to a given turning angle. This maximum turning angle defines the minimum turning radius of the tractor for a given wheel base length and tread spacing. The selection of the length of the wheel base, i.e., the distance between the fixed axle and the steering axle, is a compromise between the need to minimize the turning radius and, therefore, minimize the wheel base length, and to maximize ride considerations which require longer wheel base lengths.
Because of the size and orientation of the axle support and oscillation components, known compound steering mechanisms, such as found in U.S. Pat. No. 5,297,648, granted on Mar. 29, 1994, to C. A. Hansen and J. C. Hurlburt, are not well suited for small tractors, particularly when front hitch and front PTO applications are desired. Likewise, the oscillation stop mechanism shown in the aforementioned U.S. Pat. No. 5,297,648, and for which U.S. Pat. No. 5,322,309, granted Jun. 21, 1994, to J. C. Hurlburt, is not well suited to compact tractors because of the size of the related components. Economy is also a major concern with small tractors as the incremental cost of providing a compound steering mechanism and an associated oscillation stop apparatus becomes a greater percentage of the overall cost of the small tractor. By providing a compact oscillation stop mechanism immediately behind the front axle, a front-mounted attachment could be brought closer to the axle and economies maintained.